In a wireless communication network, users having wireless communication devices, such as for example User Equipments, UEs, mobile telephones, laptops, Personal Digital Assistance, PDA, devices may move around within a coverage area of the wireless communication network. As the coverage area of the wireless communication network comprises a plurality of RBSs, each having respective coverage areas, generally referred to as cells, the wireless communication network comprises a plurality of size-limited cells. When users of wireless devices move around, they typically go from one cell to another. The RBS typically has a limited amount of resources, e.g. with regards to radio resources, such that the RBS may be more or less loaded with traffic generated by the wireless devices. Users may be travelling in groups, e.g. on a bus or a train, at a relatively high speed, wherein the conditions for an RBS may change rapidly, e.g. a train having a plurality of passengers using their individual wireless devices entering or leaving the cell of the RBS.
Different wireless technologies, such as for example Long Term Evolution, LTE, Universal Mobile Telecommunications System, UMTS, or Global System for Mobile Communications, GSM, may have different methods for dealing with situations where an RBS becomes heavily loaded or experiences high interference.
In LTE, UpLink Power Control, ULPC, is used to adjust the power transmitted by the terminal to adapt to: a) radio propagation channel conditions, including pathloss, shadowing and fast fading, and b) interference from other users served by surrounding cells. Thus, network performance is improved in terms of retainability (i.e. dropped connection rate) and minimum/average/peak user throughput.
Third Generation Partnership Project, 3GPP, standards specify the ULPC scheme for Physical Uplink Shared Channel, PUSCH, in LTE. Such a scheme is based on the combination of two mechanisms, namely open-loop and closed-loop operation. The basic open-loop operating point is defined as
                                          P                          TX                              open                -                loop                                              =                                    P              0                        +                          α              ·                              PL                ⁡                                  [                                      dBm                    PRB                                    ]                                                                    ,                            (        1        )            where PTxopen-loop is the UE transmit power in a single Physical Resource Block (PRB) whose objective is to compensate for slow channel variations. P0 defines the average received signal level target for all UEs in a cell, PL are the propagation losses and a is the channel pathloss compensation factor. In parallel, the closed-loop operation is added to adapt UE to changes in the inter-cell interference, and/or measurement and power amplifier errors. The closed-loop operation is defined asDynamic offsetclosed-loop=ΔTF+ƒ(ΔTPC)[dB],  (2)where Dynamic offsetclosed-loop is an additional power term to add to PTXopen-loop. Its value depends on the selected modulation scheme (ΔTF) and power-control commands sent by the eNodeB (ΔTPC) according to a function ƒ( ).
Thus, the power control scheme for PUSCH including open-loop and closed-loop mechanisms calculates the UE transmit power (PTX) in each subframe as
                                          P            TX                    =                      min            ⁢                                                  ⁢                                          {                                                      P                                          tx                                                                                                                        ⁢                        max                                                                              ,                                                                                                              P                          0                                                +                                                  α                          ·                          PL                                                                                            ︸                                                                                                            basic                              ⁢                                                                                                                          ⁢                              open                                                        ⁢                                                                                                                  -                            loop                                                                                operating                            ⁢                                                                                                                  ⁢                            point                                                                                                                +                                                                                                                                            ⁢                                                                              Δ                            TF                                                    +                                                      f                            ⁢                                                          (                                                              Δ                                TPC                                                            )                                                                                                                                                  ︸                                                  dynamic                          ⁢                                                                                                          ⁢                          offset                                                                                      +                                                                                  ⁢                                                                                  ⁢                                                                                            10                          ·                                                      log                            10                                                                          ⁢                                                  M                          PUSCH                                                                                            ︸                                                  bandwidth                          ⁢                                                                                                          ⁢                          factor                                                                                                                    }                            [                                                          ⁢              dBm              ]                                      ,                            (        3        )            where Ptxmax is the maximum UE transmit power and MPUSCH is the number of allocated PRBs to the wireless device.
Several self-tuning algorithms have been proposed for the ULPC scheme, mainly by changing P0 and/or a parameters. For example, analysis of basic open-loop fractional power control (i.e. an initial setting for ULPC), or studies of close-loop operation. In such solutions, the a parameter is changed in order to mitigate interference and achieve a trade-off between overall network spectral efficiency and cell-edge bit rates. More refined power control schemes for LTE consider interference and load data. A suboptimal parameter configuration is another example for interference and noise limited macro-cellular scenarios, where P0 and α modifications are carried out to evaluate their impact on the Signal-to-Interference plus Noise Ratio, SINR, and interference distributions. Therefore, this solution uses system-level simulations to evaluate network sensitivity to changes in ULPC parameters in the standardised power control. A more sophisticated planning method may be obtained by the application of classical optimisation techniques to ULPC in a single cell, being average and cell throughput the figures of merit based on the target SINR at the desired radio base station, RBS. This method may be extended to a scenario with multiple cells using P0 adjustments, where ULPC is formulated as a non-cooperative game model and a heuristic iterative optimisation algorithm is presented (network management system is informed of uplink power settings of each cell, and there is an exchange of power and interference information among neighbour cells). Another solution is to use an overload indicator to dynamically adjust P0 parameter, and thus control the overall interference in the network. Another algorithm for ULPC that varies a parameter may be based on fuzzy-reinforcement learning techniques.
Congestion is one of the key issues in live cellular networks. Cellular traffic is unevenly distributed in time and space, which makes network dimensioning a very challenging task. As a result, some cells or RBSs in the real network may be congested, while others may be underutilised. Fast fluctuations in traffic demand are dealt with through Radio Resource Management, RRM, procedures, such as dynamic load sharing, which takes advantage of overlapping between neighbour RBSs or cells by redirecting calls to cells with available spare capacity. In contrast, localised and persistent congestion problems may solved in long term by planning strategies, such as adding new carriers or sites, or splitting cells. In the short term, the adaptation of cell service areas remains the only solution for those RBSs or cells that cannot be upgraded quickly or simply do not justify the deployment of additional resources. To adjust cell service areas, several techniques have been proposed. Some modify physical parameters in the base station, such as base station transmit power or antenna pattern. Others modify parameters in RRM processes, such as Cell (Re)Selection, CRS, and HandOver, HO. As tuning CRS parameters is only effective during call set-up, the optimisation of HO parameters, such as HO margins, is the preferred option.
The methods known in the art for adjusting ULPC settings are focused on improving user connection quality and/or reducing interference problems, but not on solving congestion problems. In an example, an Overload Indicator OI, which is exchanged between RBS, is used for inter-cell interference coordination, ICIC, when the Interference over Thermal, IoT, level is higher than a threshold. Each RBS or cell counts the number of OI messages received from its neighbours during a certain time window, and dynamically adjusts P0. Therefore, this indicator reports to a cell receiving a lot of OI messages that its neighbouring RBSs or cells have much interference due to high load. When this happens, P0 is decreased to reduce the interference. Although this mechanism detects overload, its aim is to avoid interference problems, but not to relieve congestion. In fact, the P0 parameter is reduced in surrounding RBSs or cells, and not in the RBS or cell with OI.
To solve congestion problems, methods in prior art rely on the overlapping between adjacent RBSs/cells. Thus, users, i.e. wireless devices, in a congested RBS/cell are re-allocated to surrounding RBSs/cells with spare capacity by changing antenna tilts or handover margins. Down-tilting the antenna of a congested RBS/cell may cause coverage holes in that cell. This may only be avoided if antenna changes are coordinated between neighbour sites, which are a complex mechanism. As these actions might affect coverage, they are seldom used. Likewise, decreasing HO margins in a congested cell has a negative impact on signal quality, as users, i.e. wireless devices, are not served by the RBS/cell providing the best signal level. Our first field trials have shown that the connection quality degradation produced by HO-based load balancing is dramatic in live LTE networks, where a full frequency reuse is used. The result is an unacceptable impairment in retainability.
Moreover, the congestion relief effect achieved by the previous techniques is large only if: a) the overlapping area between adjacent cells is large, and b) the traffic load pattern is uncorrelated between the cell sending traffic (i.e. congested RBS/cell) and the cell capturing traffic (i.e. empty cell). Both conditions must be fulfilled for an effective load balancing mechanism. None of these conditions is satisfied in indoor cells in urban hot-spots, especially in the underground. In this scenario, cell overlapping area is small, when compared to the cell service area, due to good isolation between cells. More importantly, the traffic load pattern between neighbour cells is fully correlated, because of user mobility in groups. As users having wireless devices travel together from one RBS to the next, users move away from the serving RBS, causing that cell load increases, as a result of using less effective modulation schemes owing to decreasing signal level. At the same time, users entering the new cell are connected very far from the new cell, producing an increase in cell load. Such a simultaneous load increase in both cells leads to an increase in received interference levels in both cells, which increases cell load even more. As a result, both accessibility, retainability and user throughput degrade significantly. Retainability figures (i.e. dropped connection rate) may grow up to 75% in these cells. Note that this situation cannot be solved by dynamic load sharing algorithms based on temporarily changing HO margins, as cell overlapping proves to be not enough.